Utilizing Stable Isotopes and Major Ions to Isolate the Recharge Regime of an Alluvial-Proluvial Fan Aquifer in the Piedmont Region of the South Taihang Mountains, North China Plain

Abstract

A thorough understanding of groundwater recharge is critical for sustainable groundwater development in semi-arid areas. To determine the recharge regime in one alluvial-proluvial fan aquifer which usually acts as the main recharge zone of its local groundwater, field surveys and isotopic analyses were conducted in the piedmont region of the South Taihang Mountains of the North China Plain during the rainy (August) and dry (November) seasons. Precipitation could not effectively provide short-term recharge to the alluvial-proluvial fan aquifer due to the deep water table. The fault buried by the mountain front alluvial-proluvial deposits acts as a barrier, inhibiting effective recharge to the overlying Quaternary aquifer. Sulfate concentration and isotopes were more elevated in deep groundwater of the alluvial-proluvial fan area compared to that in the depression region, suggesting that lower deep groundwater potential has resulted in the inter-aquifer flow from the shallow alluvial-proluvial fan aquifer feeding the deep aquifer underneath. Inter-aquifer leakage showed an inverse relationship with the distance from the mountain edge, and its recharge may be influenced by the distribution of the aquitard in the deep aquifer of the proximal fan, leading to a decreased contribution of inter-aquifer leakage. Additionally, the deep groundwater flow in the Sha River alluvial-proluvial fan is disturbed by the hydraulic potential decline in the proximal fan region, as exhibited by a more complex flow pattern and reduced groundwater mixing zone. Our results increase understanding of piedmont hydrology and the management of its related water resources.